Concordance between two methods in measuring treatment adherence in patients with type 2 diabetes

We analyzed the concordance between two methods for measuring treatment adherence (TA) and studied the determinants of TA in patients with type 2 diabetes mellitus.

We conducted a cross-sectional descriptive study in a primary care center, involving 320 diabetic patients. TA was measured using the Haynes-Sackett (H-S) adherence test during the patient interview and based on pharmacy refill data. TA was calculated globally and by drug groups (antihypertensive, lipid-lowering, and antidiabetic drugs).

Poor TA as measured by the H-S test was observed in 11.2% of the patients. Based on pharmacy refill data, there was a poor global TA rate of 30.3%, which was 33.3%, 26.6%, and 34.2% for oral antidiabetic, antihypertensive, and lipid-lowering drugs, respectively. Concordance between the two methods was poor. There was no relationship between the degree of disease control and TA as measured by the H-S test. Good TA measured based on pharmacy refill data for antidiabetic and antihypertensive drugs was associated with lower glycosylated hemoglobin and diastolic blood pressure values, respectively. Patients with good global TA showed lower glycosylated hemoglobin, diastolic blood pressure, and low-density lipoprotein cholesterol values. The multivariate analysis found good oral antidiabetic adherence to be associated to free pharmacy service; good antihypertensive drug adherence to the existence of comorbidities; and good lipid-lowering drug adherence to a history of ischemic heart disease, and a more experienced physician and/or female physician.

Concordance between the two methods in assessing TA was low. Approximately one-third of the patients with type 2 diabetes mellitus presented poor TA in relation to antihypertensive, lipid-lowering, and antidiabetic medication. An improved TA was associated with a better control of the studied parameters. Comorbidities, such as ischemic heart disease and access to free pharmacy service, were identified as determinants of good TA.